The present invention generally relates to communication equipment and more particularly, to a radio frequency signal combining/sorting device.
The radio frequency signal combining/sorting device referred to in connection with the present invention includes an antenna sharing device, diplexer, a duplexer, unit exclusively for sorting, or a unit exclusively for combining, etc., and hereinafter, will be described with reference to a transmitter multiplexer as an example.
Conventionally, in an antenna sharing device at a base station for an automobile telephone or the like, it has been a practice to compose a plurality of frequency signals by means of a transmitter multiplexer for transmission from one antenna through an antenna line, and for such a transmitter multiplexer there has been available an arrangement, for example, as shown in FIG. 3, which includes a plurality of channel filters 30 (two channel filters are shown in FIG. 3) respectively having different resonance frequency signals, and a duplexer means 31.
In the above known arrangement, for the channel filters 30, for example, magnetic coupling type TE.sub.01 .delta. dielectric resonators and the like are employed, with coupling loops 32 disposed within the resonators and externally led out therefrom through connectors 33. On the other hand, in the duplexer means 31 through which a composite transmission line 34 extends, connectors 35 are provided for connection with the connectors 33 referred to above, and these connectors 35 are connected to the composite transmission line 34 through an individual transmission line 36.
For these connectors 33 and 35, push-on type connectors, etc. are employed to facilitate connection therebetween, whereby both of the connectors 33 and 35 are arranged to be connected to each other by inserting the connectors 33 of the respective channel filters 30 into the connectors 35 of said duplexer means 31.
However, the conventional transmitter multiplexer explained so far has problems as described hereinbelow.
Specifically, since the channel filters 30 and the duplexer means 31 are mechanically connected to each other by the connectors 33 and 35, contact resistance is present at portions of such connectors. Therefore, joule loss is caused by the contact resistance, etc. at such connector portions, and the electrical characteristics of the device undesirably impaired.
There are certain desirable characteristics for an electrical length of the individual transmission line 36 from a junction of the composite transmission line 34 and the individual transmission line 36 in the duplexer means 31, i.e., from a so-called junction point 37 including the coupling loops 32. This electrical length should preferably be stable at 1/4 wavelength, i.e., an electrical angle of 90 degrees, on the assumption that the channel filters 30 are not coupled with the duplexer means 31 at the required center frequency of the frequency band region of the transmission sharing device. However, the problem exists that this electrical length becomes unstable and undesirably scatters (varies unpredictably), depending on the state of connection at the connector portions.
Such problems as described above arise in other radio frequency signal composing/sorting devices as well.